1. Field of the Invention
This invention relates to an automatic flash light device for a photographic camera, and more particularly to an automatic flash light control device for a camera having both an automatic flash light device and an interchangeable taking lens.
2. Description of the Prior Art
In conventional single lens reflux cameras having an interchangeable lens and provided with an automatic flash light device, the diaphragm aperture of the taking lens is predetermined according to the film sensitivity of the film in the camera, and the amount of light emitted by the electronic flash light device is controlled to obtain a desirable exposure in combination with the predetermined diaphragm aperture. Therefore, in a camera provided with the conventional automatic flash light device, the size of the diaphragm aperture is automatically determined according to the sensitivity of the film when the flash light is used. This is disadvantageous because it results in the focal depth, which depends upon the aperture size, also being automatically determined, and accordingly, it is impossible with such a camera to freely select the focal depth where pictures are taken under flash light condition.
In order to solve the above mentioned problem, it is possible to introduce information regarding the proper diaphragm aperture into the automatic flash light device together with information regarding the film sensitivity, so that the amount of light emitted by the electronic flash light device is controlled according to both the proper diaphragm aperture size and the film sensitivity of the film in the camera.
However, in a single lens reflex camera with an interchangeable taking lens of diaphragm aperture priority mode, the shutter speed control circuit is provided with a full aperture light measuring means or a stopped down aperture light measuring means. Therefore, the information regarding the diaphragm aperture in this type of camera is represented by a value corresponding to the displacement from the full aperture. Accordingly, when the amount of light emitted by the electronic flash light device in the automatic flash light device is controlled according to the information which normally represents the aperture size in the camera in terms of the displacement of the aperture size from the full aperture, the finally controlled amount of light will change as the full aperture size changes in different taking lenses. In other words, even when the same aperture size is selected in different cameras or lenses, the resulting amount of light emitted by the controlled electronic flash light device will change if the full aperture sizes of the lenses are different from each other.